Some Recent Work on Hybrids in Plants. 79 
possible combinations of the gametes of the hybrid is given by the 
combinations of the two series :— 
A -+- 2 Aa + a and B 2 B b b. 
The number of different combinations so produced is nine, and 
of these nine combinations four should each occur once, four should 
each occur twice and one should occur four times in every 16 plants. 
In the actual experiment the number of different classes of forms 
which appeared was nine and they occured in the proportion deduced 
above from the theory. Similarly when races with three pairs of 
differentiating characters are crossed, twenty-seven classes are to 
be expected from a combination of the series:— 
A + 2 A a -f a, B ff- 2 Bb -f b, C + 2 Cc -f c. 
In the actual experiment twenty-seven classes of forms occurred, 
and that in the proportion to be expected from the theory. 
Mendel attempted to put his theory to further experimental 
proof by crossing a hybrid, produced from parent races with two 
pairs of differentiating characters, with both its parents and using 
alternately hybrid and parent as male and female. The four series 
of experiments may graphically be written in terms of the gametes 
thus:— 
(i.) JAB, ?Ab, ?aB, Jab X c? A B. 
(ii.) J A B, 5 A b, J a B ?ab x c?ab. 
(iii) ?A B x $ A B, $ A b, $ a B, $ a b. 
(iv.) ?ab x d'AB, Mb, cf a B, ^ab. 
It is clear that in each of the experiments four classes of forms 
should appear, and that those of the first and third should be 
exactly like those of the second and fourth experiments. Further¬ 
more if the several forms of male and female gametes of the hybrids 
are produced on an average in equal numbers then all the classes of 
form should occur in the same numerical proportion. All the forms 
which the theory demands were produced, and in approximately 
equal numbers. 
Mendel’s results have been largely confirmed by Tschermak (’ 00 ) 
and Correns (’OOa)forPea Hybrids,and by DeVries (’ 00 a) in a number 
of cases other than Peas. It is interesting to note that De Vries 
seems to have arrived independently at the same view of the separation 
of the characters of the sexual cells, at a time when, in common with 
other botanists, he had overlooked the existence of Mendel’s work. 
The two outstanding results of Mendel’s work are the law of 
dominance (the Pravalenzregel of Correns), and the law as to 
separation of the character in the gametes of the hybrid, which 
